You can use a 1G SFP or SPF+ port as a VC port but I don't think you can use a 1000BASE-T port as a VC link.
http://www.juniper.net/techpubs/en_US/junos11.3/topics/task/configuration/virtual-chassis-ex4200-uplink-vcp-cli.html
"You can interconnect EX4200 switches that are beyond the reach of the Virtual Chassis cables as members of a Virtual Chassis configuration by using the SFP network ports—including the SFP uplink module, SFP+ uplink module, or XFP uplink module—and connecting the uplink ports . You can also use the SFP network ports for this purpose. To use the uplink ports or SFP network ports for interconnecting member switches, you must explicitly set the uplink ports as VCPs.
Note: You cannot set a 1000BASE-T copper SFP transceiver (EX-SFP-1GE-T) connection as a VCP."